Engines or motor which generate power typically transfer this power through an angularly rotating shaft. Similarly, hand operated machines typically have power input through an angularly rotated shaft or crank. It is frequently necessary to convert this rotary motion to translatory motion to perform a particular function. This conversion can be accomplished through means known in the art such as a rack and pinion gear arrangement, a threaded screw and nut, a drive wheel and belt, etc. The threaded screws and nuts of the prior art have been improved by incorporating ball bearings into the nuts to reduce friction losses.
The devices of the prior art have numerous disadvantages such as high cost, short service life and mechanical inefficiency. The inefficiency tends to increase with increasing load transferred.
It is known in the art that a roller in contact with a shaft such that the longitudinal axis of the roller is skewed at an acute angle with the longitudinal axis of the shaft will rotate and move the direction of the shaft's longitudinal axis when the shaft is angularly rotated. Conversely, when the roller is angularly rotated, the shaft will move in a translational manner. For example, U.S. Pat. No. 3,081,639 discloses a mechanism containing skewed rollers for moving a shaft, wherein the mechanism is rotated about the nonrotatable shaft, thereby causing the shaft to move in a linear fashion. U.S. Pat. No. 3,990,317 discloses a wire feeding mechanism comprising inclined or skewed rollers in a frame. Rotation of the frame about a wire causes the wire to move linearly through the central channel of the frame. U.S. Pat. No. 4,131,028 similarly discloses a motion conversion mechanism for moving wire, wherein the skewed rollers in contact with the wire are driven by separate drive rollers. These motion conversion devices of the prior art have numerous disadvantages including complex drive mechanisms, the need for heavy complex frames, low load limitations, inadequate roller to shaft contact, short roller life and mechanical inefficiency. In addition, the rollers of the prior art are either coiled wire rollers or flexible rollers which do not have high load handling ability or service life.
Accordingly, what is needed in this art is an apparatus for converting rotary motion to translatory motion, or translatory motion to rotary motion, which has a minimum number of parts, a simple frame, long-life rollers, high efficiency and which can withstand heavy loads.